1. Field of the Invention
The invention relates to a method for the passivation of silicon components provided with aluminum metallization, by applying at least one silicon layer.
2. Description of the Prior Art
It is known to passivate the surface of semiconductor components for the stabilization of current/voltage characteristics by applying various organic or inorganic cover films. By means of such cover films which may consist of paints, rubbers, or glasses, for example, it is generally possible to obtain characteristics of sufficient stability. At times, however, instabilities occur, the causes of which can be traced to changes in the properties of the cover films and/or of the component surface and which can lead to serious variations in the yield of usable components.
A method to passivate a semiconductor element by having a silicon layer grow on it thermally has been described. This method, however, is relatively time-comsuming and costly. It also requires high temperatures.
From German Published Non-Prosecuted Application DE-OS No. 26 32 647 is known a passivating method in which the protective layer consists of vapor-deposited silicon. This results in stable characteristics at considerably less expense. In addition, it is known from German Published Non-Prosecuted Application DE-OS No. 27 30 367 that, in the case of passivation by means of a vapor-deposited silicon film, the cut-off current in the cut-off direction and the reverse current in conduction direction of a semiconductor component can be lowered drastically by an annealing operation. Particularly good results are achievable when tempering takes place in an atmosphere containing oxygen.
The passivating method known from German DE-OS No. 26 32 647 and German DE-OS No. 27 30 367 is commonly called the EPOS (Evaporated Polysilicon on Surface) method. Therefore, a polycrystalline silicon layer vapor-deposited by this method is hereinafter called "EPOS" for short.
If such a silicon layer is vapor-deposited on a silicon wafer already provided with a metallization, it requires technological measures to remove the vapor-deposited silicon from the contact areas of the components or make them contactable. This is usually accomplished by protecting the contact areas of the components to be vapor-deposited by masking such as by means of photoresist or a perforated mask (shadow mask) or if the EPOS film is removed from the contact areas after the vapor-deposition by selective etching. However, appropriate measures are not without problems. Production engineering-wise, the selective etching of the photoresist-masked passivation film in particular is of significance. But due to masking problems at mesial edges and due to the attach on the metal surface, the passivation or the subsequent contact-making ability can be disturbed considerably.
These problems can be avoided if chips already soldered and contacted are passivated so that no masking or selective etching is required. But such a procedure is relatively expensive, especially for small chip sizes. Also, the passivation can be influenced by masking effects caused by the contact wires.